This invention relates to novel processes for adhering polymeric hydrogels to an adhesive coated surface of a substrate and to novel hydrogel laminates and bandages and methods for forming the same.
The integumentary system is the exterior organ that, although often taken for granted, is vital to physical well being. The most obvious function of the integument is to protect against infection. Any alteration in the integrity of the skin compromises this natural defense. To minimize the risk of soft tissue infection, it is desirable to protect burns and wounds from infectious agents such as airborne fungi, bacteria and viruses. Traditional gauze type dressings are inadequate because they do not exclude infectious agents. Further, exudation from many types of skin lesions is normal during the healing process. If wound exudate has dried and consolidated the gauze dressing and wound, removal of the dressing is not only painful, it interferes with the healing process.
The use of hydrogels in the treatment and management of burns and wounds is well known in the art. Hydroqel dressings are desirable, in part, because they provide protection against infectious agents. Hydrogel dressings are further desirable because wound exudate does not generally dry and consolidate with hydrogels or hydrogel laminates. Consequently, removal of a hydrogel dressing is usually neither painful nor detrimental to the healing process. It has been suggested that hydrogel dressings may be particularly desirable for treatment of burns because they may accelerate healing. Although the mechanism by which hydrogels stimulate healing is not fully elucidated, it is documented that the high water content of hydrogels enables them to effect an immediate cooling of the wound surface and to sustain the reduced temperature for up to six hours. Davis, et al., xe2x80x9cA New Hydrogel Dressing Accelerates Second-Degree Burn Wound Healing,xe2x80x9d Poster Presentation, Wound Healing Society First Annual Meeting, Galveston, Tex., Feb. 6, 1991. In addition, water swollen hydrogels may provide a cushioning effect that helps protect the burn or wound from physical trauma.
U.S. Pat. No. 4,438,258 relates to hydrogels which may be used as interfaces between damaged skin tissue and its external environment. As disclosed therein, hydrogels may be polymerized about some type of support, such as a mesh of nylon, used as an unsupported film, spun in fibers and woven into a fabric, or used as a powder. Further, hydrogels may be used to provide a controlled release of a medical composition.
U.S. Pat. No. 4,552,138 discloses a wound dressing material of at least one layer of a polymeric, hydrophilic gel wherein the gel is cross-linked and acetalized with formaldehyde. As disclosed therein, a gel film may be formed by spreading a pre-crosslinked gel on an auxiliary carrier, drying and at the same time cross-linking the same by heat treatment. As used in this disclosure, un-crosslinked polyvinyl alcohol is dissolved in water, acidified, preferably by hydrochloric acid, and combined with an aqueous formaldehyde solution and left to react or pre-crosslink at 50-80xc2x0 C. for several hours to obtain a gelatinous mass wherein no further free aldehyde can be detected. Such gel films may be placed on the wound as such, but they are preferably processed to a laminated product with one or more carrier materials and used in this form. The carrier layers are laminated into or onto the pre-crosslinked gel layer and may be further cross-linked to bond more firmly with the gel.
U.S. Pat. No. 4,554,317 discloses a synthetic hydrophilic membrane prepared by graft polymerization of hydrophilic monomers with a polyurethane substrate. This membrane is particularly useful as a wound covering material. In one embodiment of this invention, the graft polymerization is initiated by X-ray or gamma radiation or an initiator such as a cerium salt.
EPO Publication No. 0 107 376 A1 discloses a tacky, non-rigid transparent and absorbent dressing comprising a layer of cross-linked polyvinylpyrrolidone gel containing from about 75-85% water. The dressing may be prepared by dissolving between 15% and 25% by weight of polyvinylpyrrolidone in water and cross-linking the polyvinylpyrrolidone by means of ionizing radiation.
U.S. Pat. No. 4,567,006 discloses a moisture vapor permeable, adhesive surgical dressing comprising a continuous film of a hydrophilic polymer. Such a dressing is suitable for use on moist wounds because it allows water to evaporate rapidly from the wound area in the presence of an excess of exudate but, as the amount of exudate diminishes, so does the rate of evaporation. The resulting amount of exudate is enough to keep the wound moist without causing blistering of the dressing.
U.S. Pat. No. 4,798,201 discloses a surgical dressing consisting essentially of a film which carries an adhesive layer for securing the dressing to the body. This dressing is also suitable for use on exuding wounds.
U.S. Pat. No. 4,407,846 discloses a method of producing a hydrophilic membrane from a polyethylene base film by first irradiating the film of thickness not more than 150 xcexcm with ionizing radiation in air or an oxygen atmosphere. Then, without additional radiation, acrylic acid and/or methacrylic acid present in the form of an aqueous solution is grafted onto the irradiated film.
U.S. Pat. No. 3,669,103 discloses a flexible support adapted to be caused to conform to a surface of a body, wherein the support confines a dry, solid, water-swellable, water-insoluble polymeric sorbent to absorb aqueous fluid elaborated by the body to which the support is applied. The polymer sorbent is a lightly cross-linked polymer.
U.S. Pat. No. 4,192,727 discloses a polyelectrolyte hydrogel and method for preparing the same. The polyelectrolyte hydrogel is formed by exposing an acrylate salt and acrylamide to a controlled intensity and dose of ionizing radiation to effect simultaneous cross-linking and polymerization thereof. The resulting hydrogel is an insoluble hydrophilic copolymer which can contain or absorb aqueous fluid.
U.S. Pat. No. 4,646,730 discloses a color stabilized sulfadiazine hydrogel dressing comprising a non-rigid layer of cross-linked polyvinylpyrrolidone gel having incorporated therein at least 0.1% by weight of silver sulfadiazine, which gel has been exposed to electron beam radiation and which gel also contains a color stabilizing amount of magnesium trisilicate.
U.S. Pat. No. 4,750,482 discloses a wound or burn dressing comprising a web-like substrate coated with a layer of crosslinked, water-insoluble, hydrophilic, elastomeric, pressure-sensitive adhesive gel of a gel-forming, water-soluble polymer derived from repeating units, predominantly of vinylpyrrolidone, polyethylene glycol wherein the cross-linked gel is formed by radiation cross-linking of a solution or dispersion of the polymer in the plasticizer and water. The gel retains the plasticizer within a cross-linked three-dimensional matrix of the polymer.
EPO Publication number 0 304 536 A2 discloses an occlusive wound dressing comprising an adhesive layer, a fabric layer bonded to the adhesive layer, a hydrophilic absorbent polymeric layer applied to the fabric layer, and at least one occlusive backing layer. The hydrophilic absorbent polymeric layer of this dressing is applied by pouring a monomer solution onto the fabric layer and thereafter curing to yield the polymeric layer.
Japanese Patent Application No. 57-7414 issued in the name of Saburo Otsuka and assigned to Nitto Electric Ind. KK, discloses a medicinal plaster formed by spraying or spreading a solution or dispersion containing a monomer, a medicine, a releasing aid for medicine, etc., on the surface of a tacky layer formed on a support, and then irradiating it with UV or ionizing radiation.
U.S. Pat. No. 4,871,490 discloses a method of manufacturing hydrogel dressing from synthetic and natural polymers by radiation cross-linking. The method involves an aqueous solution comprising 2-10% by weight polyvinylpyrrolidone, no more than 3% by weight of agar and 1-3% by weight of polyethylene glycol. The solution is poured into a mould to shape the dressing. The mould is then tightly closed and subjected to an ionizing radiation dose in the range of 25-40 KGy.
At present, there are a few commercially available hydrogel dressings, for example, Second Skin from Spenco and Vigilon from C. R. Bard. However, a significant problem with hydrogel dressings is that the high water content of the hydrogel makes a good adhesion with a substrate problematic. Failure to establish an adequate bond between the hydrogel and the substrate may lead to delamination and failure of the product. Consequently, currently available hydrogel dressings utilize a secondary dressing to keep the hydrogel in place. This is both inefficient and costly. It also makes the product hard to use on certain body areas. Accordingly, there is a need for adhesive bandages having a hydrogel pad securely adhered to a substrate and for processes by which a polymeric hydrogel can be securely adhered to a substrate.
It is an object of this invention to provide hydrogel laminates with improved delamination resistance and processes by which a polymeric hydrogel can be securely adhered to an adhesive coated surface of a substrate. It is a further object of this invention to develop improved adhesive bandages having absorbent hydrogel pads.
These objects have been met with the present invention. This invention relates to a hydrogel laminate comprising a substrate, such as a moisture impermeable film, a layer of polymeric adhesive on at least one surface of said substrate, and, adjacent to said adhesive coating, a layer of hydrogel. The hydrogel is formed by crosslinking of one or more hydrophilic polymers. The hydrophilic polymer(s) which form the hydrogel and the base polymer(s) of the adhesive are selected so that the these polymers are capable of copolymerizing with one another, for example, upon exposure to ionizing irradiation. The laminate so formed may be used as a component in a bandage for wound dressing, and, because of the excellent delamination strength of the laminate, such bandages offer advantages over hydrogel dressings previously known.
This invention also relate to a process for forming a hydrogel laminate. In this process, a substrate is coated on at least one surface with one or more polymeric adhesives. An aqueous solution of one or more hydrophilic polymers is cast onto the coated surface of the substrate, and the resulting composite is exposed to ionizing irradiation suitable to cross-link the hydrophilic polymers to form a hydrogel and to copolymerize the base polymers of the hydrogel and of the polymeric adhesive.